双戗堤截流时下戗堤的作用分析

On Function of Downstream Closure Dike under Vertical Closure with Two Dikes

立堵截流计算的核心内容是龙口流速的求取 ,因为龙口流速的大小直接影响到截流时所选择抛投料粒径的大小 ,可以说是衡量截流难度的一个重要指标。本文在分析单戗堤立堵截流龙口流速变化规律的基础上 ,着重研究了在双戗堤立堵截流中 ,当上戗堤最困难的时候 ,也就是流速最大的时候 ,下戗堤是否能够壅水 ,从而降低上戗堤的截流难度这个问题 ,论证了双戗堤立堵截流水力控制条件的正确性 。

One of key problems in vertical closure calculation is to obtain flow velocity through the closure gap because it directly influences grain size of the rock blocks damped for the river closure and is also an important index for judging difficulty to cut off the river.On the basis of analyzing regularity of variation of flow velocity through the closure gap under vertical closure with single closure dike,this paper studies the problem under verticle closure with double colsure dikes (one upstream and one downstream) in particular whether the downstream closure dike can dam up the water level to reduce difficulty for the upstream dike closure when the flow velocity through the upstream closure gap reaches its peak value.The paper demonstrates the correctness of hydraulic control condition under verticle closure with two closure dikes and provides judgement criterion for successful vertical closure of river using two closure dikes.